Binary cycle power plant having a high melting point tertiary fluid for indirect heating



L. R. BIGGS ER' PL Aprd 22, 1952 BINARY CYCLE Pow ANT HAVING A HIGHMELTING POINT TERTIARY FLUID FCR INDIRECT HEATING Filed Jan. 11, 195o8., E C oB..m A o d ,t er .t Va A .mm e N L VJ Patented Apr. 22, 1952UNITED STATES OFFICE Leonard R. Biggs, Schenectady, N. Y., assignor toGeneral Electric Company, a corporation of New York Application Januaryil, 1950, Serial No. 137,993

(Cl. Sii- 38) Claims. 1

This invention relates to thermal powerplants, particularly to apowerplant of the type having three separate uid circuits, one of whichis charged with a liquid which never reaches its boiling point, whilethe other two contain suitable liquids of a type which pass throughliquid Y `and vapor phases as in more conventional elastic fluid turbinepowerplants.

An object of the invention is to provide a thermal .powerplantespecially adapted to extract thermal energy from a heat releasingreaction of extremely high intensity and occupying a comparatively smallvolume, and converting this thermal energy to mechanical energy with themaximum possible efliciency. Another object is to provide a thermalpowerplant of the type described in which the primary liquid circuitincludes only a single supply conduit and a single return conduitconnecting a primary heating dcvice with heat exchangers which transferenergy to the secondary and tertiary fluid circuits, so that thesecondary and tertiary circuits with their respective heaters may belocated at a considerable distance from the heat generating reaction,without complex piping therebetween. A still further object is toprovide a three iiuid powerplant in which the components operating atthe highest temperature levels in the cycle also operate at a lowpressure, so that the mechanical strength and life of the components maybe adequate. Another object is to provide an improved powerplantarrangement having even greater thermal eliiciency than previously knownbinary Huid powerplants, yet requiring a smaller charge of operatingliquid.

Other objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawing in whichthe single ligure represents schematically the a1'- rangement oi a threeuid powerplant in accordance with the invention.

Referring now more particularly to the draw ing, the heat generatingreaction is represented to be the combustion of a suitable fuel in aboiler indicated generally at I as including a combustion chamber 2lined with boiler tubes 3 and hav ing a suitable fuel burning device fl.Combustion air is supplied by a forced draft ian 5 through an airpre-heater 6 in accordance with conventional practice. The ue gases aredrawn from the combustion space through a liquid pre-heater oreconomizer l and the air pre-heater 6 by an induced draft fan 8. Whilethis rather conventional type of boiler arrangement has been disn closedfor purposesof illustration, itis to be noted teiial.

t 2 i v that the present powerplant is particularly adapted forextracting and converting thermal energy from heat generation devices oimuch more compact design which liberate energy at rates far exceedingthose found in the ordinary steam boiler. For instance, a gas turbinecombustor of the general type disclosed in the copending application ofA. J. Nerad, Serial No. 750,015, led May V23, i9fl7,`and assigned to thesame assignee `as the present application, might well be used as theheat generating device. In such a combustor, heat release space rateswell above 5,000,000 B. t. u. per hour per cubic foot of combustionspace volume may be obtained. Other heating means of very high intensitytypes will occur to those skilled in the art.

The primary fluid circuit is indicated by the solid arrows in thedrawing. t is to be particularly noted that this primary circuit ischarged with a material which remains liquid in all parts of thecircuit, the temperatures in the heat generator being below thoserequired to boil the ma- 'ihis charge may consist of liquid sodiummetal, which melts at 208 F., or any one of several known mixtures ofsodium salts, such as those previously used in the so-called saltcooledexhaust valves oi internal combustion enlt is also to be particularlynoted that the pressure in this primary circuit is comparatively low,the static pressure being only that resulting from the hydraulic head`due to diilerences in level of the various parts of the circuit. Tokeep the primary circuit charged and to insure that the pressure doesnot rise above the static head of the liquid in the circuit, a surgetank shown at 9 is provided. rlhis is maintained at atmospheric pressureby means of the bellows 9d which freely provides expansion room toaccommodate changes in volume of the liquid charge as the operatingtemperature varies, without creating pressures above atmosphericpressure. If the primary liquid is or a type which does not decompose inContact with oxygen, the surge tank 9 may simply be vented to theatmosphere.

The heat released in the combustion space 2 is transferred to theprimary liquid in the heat generator tubes 3 and extracted in a primaryheat exchanger consisting of a series of four heat exchange devices inseries iiow relation. It will be apparent that the hot primary liquidenters the top of the heat exchange device Il. then iiows progressivelydownward through the second heat exchange device l2, the third heatexchange device i3, and the fourth heat exchange device it, from whichit is caused to circulate by the primary liquid circulating pump I5through the return conduit I6. Conduit I6' conducts the cool liquidthrough the economizer l, from which it enters the upper header 3acommunicating with the respective heater tubes 3. It will be observedthat the cool liquid ows downwardly through the tubes 3 in counter-nowrelation with the hot gases in the combustion space 2. The hot liquid iscollected by the lower header 3b which con municates with the supplyconduit Ill.

It will be observed that the` piping connecting the heat generator withthe primary heat exchanger is extremely simple, consisting of only onesupply pipe and one return pipe. Thus the primary heat exchanger can belocated immediately adjacent the turbines and their auxiliary equipment,while the heat generator may be conveniently located at a considerabledistance from the rest of the powerplant. This means that a minimumamount of very simple piping is required between the heat generator andthe heat converting equipment.

A number of important advantages may be noted in connection with theprimary liquid circuit of this pOWerplant. In the first place, the heattransfer from the combustion gases to the primary fiuid is of optimumefficiency since the liquid never boils in the primary circuit. Thismeans that the highest efficiency is obtained from the counterow heatexchange process in the heater I, since the temperature of the liquidincreases progressively as it flows downwardly, while the hot gastemperature decreases progressively as it flows upwardly past the heatertubes 3. This is in sharp contrast with the usual steam or mercuryboiler, in which there is a certain location in the tubes where theliquid phase changes kto the vapor phase, at which point considerableheat energy is absorbed without any change in temperature. Thisintroduces an inherent loss of efficiency, which is avoided with thepresent arrangement. Thus the present arrangement eliminates a seriousirreversibility which introduces substantial inherent losses in thethermal cycles of previously known mercury and steam turbinepowerplants. Furthermore, the heat transfer process from the hot gaseskthrough the metal walls of the tubes 3 to the liquid within the tubesis much more eilicient than the more usual transfer of heat fromcombustion gases through boiler tubes to a fluid which may be partlyliquid, partly vapor, and sometimes a mixture of the two.

It may also be noted that the sodium or sodium salt mixture used as theprimary liquid is much lower in cost than the mercury charge used inpreviously known binary fluid powerplants. Likewise, because of the moreefficient heat transfer, the heat generating equipment may be smaller insize and therefore cheaper.

A most important advantage lies in the fact that the primary uidcircuit, which operates at the highest temperatures occurring in thecycle, at the same time operates at a comparatively low pressure.Whereas in a mercury boiler of conventional arrangement, the boilertubes may be required to operate at pressures in the neighborhood of 500pounds per square inch, the static pressures existing in the presentsystem may be only on the order of 50 pounds per square inch gage, andeven this high a pressure will exist only in a portion of the tubes atthe lower levels in the primary circuit. Therefore, because themechanical stresses due to pressure Within the tubes are comparativelylow in those portions of the circuit where the thermal stresses arehighest, the heat transfer tubes and hot liquid conduits may be moreconveniently designed to have adequate strength and life, withreasonable safety factors.

The secondary fluid circuit is represented by the dashed arrows in thedrawing and comprises a mercury vapor turbine indicated at IS Vas beingof the well-known double-flow type. After giving up some of its energyin the turbine rotor Ilia, the mercury vapor serves to heat a fifth heatexchanger I'I, a sixth heat exchanger I8, and a seventh heat exchangerI8. It will be appreciated by those skilled in the art that these heatexchangers I?, I8, I9 may be conveniently 1ocated within an exhaustcasing common to the turbine I. Liquid mercury is withdrawn from thebottom of the turbine casing by a circulating pump 2Q, whence it flowsthrough conduit 2| to heat exchanger I8, which serves as a mercuryliquid pre-heater. From the pre-heater I8, the liquid mercury flowsthrough conduit 22 to the second heat exchanger I2 which furtherpre-heats the liquid, the mercury flowing through heater I2 incounter-flow relation with the primary iiuid. From pre-heater I2, theliquid mercury flows through conduit 23 through the rst heater II, againin counter-now relation with Vthe primary fluid. The heater il is, ofcourse, the boiler for the mercury cycle, from which mercury vaporpasses through conduit 24 to the inlet of the mercury turbine IS. Inaccordance with conventional practice, a separator drum 25 may bearranged so that any liquid particles in the conduit 24 will return tothe inlet side of the heater I I.

it will be observed that this arrangement of the mercury cyclefacilitates placing the heaters I i, I2 immediately adjacent the mercuryturbine i5, and as noted before the heaters I'I, I8, I9 are integralparts of the mercury turbine unit. Thus the mercury portion of the cyclecan contain a liquid charge of comparatively small weight, which meansthat much less of the comparatively expensive mercury is required thanis the case in conventional mercury powerplants. Likewise, the pipingconveying hot mercury from heaters to turbine is comparatively short,thus reducing the complexity and cost of the high temperature piping,also reducing the probability of accidentally releasing mercury into theatmosphere which would constitute a serious health hazard.

The tertiary fluid circuit is indicated by the dotted arrows in thedrawing. This comprises a high pressure steam turbine 26 in series witha low pressure turbine 21. The turbine 26 is of the extraction type, thesteam extracted through conduit 2B serving as the heating medium in anextraction heater Z9, as described more particularly hereinafter. Afterpassing through the rotor 21a, of the low pressure turbine, the exhauststeam passes throughsa feed-water heater 30 and then into the steamcondenser SI. Condenser 3l is of conventional construction, having asuitable coolant pump 32 for circulating watel` at a low temperaturethrough the intake conduit 32a and out the discharge conduit 32h. Itwill be noted that the heat transferred to the cooling water in thecondenser 3l is the only thermal energy Arejected in this system, asidefrom the usual radiation losses, and, of course, the sensible heat inthe flue gas from the furnace I. Also associated with condenser 3! is ahot-well or circulating pump 33 which supplies condensate to a boilerfeed pump 34. In accordance with conventional practice, a suitable typeof air ejector35 may be provided to remove any entrained air from thecondensate. Also, there may be provided in cooperation with the boilerfeed pump 34, as indicated diagrammatically at 36, a de-aerating heater,the heating medium for which is steam extracted through conduit 3I fromthe exhaust casing of the high pressure turbine 26. Condensed heatingfluid from the extraction heater 29 drains to the deaerating heater 38through conduit 38. A suitable surge tank 39, vented to the atmosphere,insures an adequate supply of liquid to the boiler feed pump, andprovides expansion room for changes in volume of the hot water in thesystem.

It will now be apparent from the drawing that the hot-well pump 33supplies water through the air ejector 35 to the feed-water heater 30,thence to the de-aerating heater 36 and the boiler feed pump 34. Pump 34circulates liquid through the extraction pre-heater 29, thence to themercury condenser-boiler I9, vwhich may be provided with a separatordrum I9a. From this separator, steam passes by way of conduit 42 tothefifth heat exchanger which serves as an extraction super-heater, whencethe super-heated steam passes through conduit 43 to the third heatexchanger I3 where it absorbs further heat in counter-flow relation withthe primary fluid. From heat exchanger I3, the highly super-heated steampasses by way of conduit 44 to the inlet of the high pressure turbine2B. The principal portion of steam exhausted from turbine 26 passes byway of conduit 45 to the fourth heat exchanger I4, which serves as areheater supplying motive uid through conduit 46 to the inlet of the lowpressure turbine 2'I.

It will be apparent from the above description that this novelpowerplant arrangement provides the most efficient form of counter-flowheat exchange in the heat generator I because the primary fluid remainsliquid throughout the heater, while at the same time thermal energy istransferred from the primary liquid to the secondary and tertiary fluidsin a series of heat exchangers which are also arranged for mosteffective utilization of the counter-flow principle. observed that theprimary liquid works at extremely high temperatures but low pressures,the tertiary uid operates at high pressures, while the secondary fluidoperates at intermediate pressures and temperatures. Thus, in general,it can be said that no component in the system is exposed to bothextremely high temperature and extremely high pressure conditions.

In the arrangement shown in the drawing, the mercury turbine I 6 and thehigh and low pressure steam turbines 26, 21 are all geared to a commonload device, shown as an electrical generator 41. The reduction ratiosbetween the respective pinions 2lb, 25a, and Ib are so selected that thehigh pressure steam turbine rotor operates at a speed in theneighborhood of 5,000 R. P. M., the low pressure turbine operates at anintermediate speed in the neighborhood of 1,800 R. P. M., while themercury turbine runs at a speed in the neighborhood of 900 R. P. M. Thusthe three different types of turbines are permitted to operate at theirmost eilicient speeds although geared at fixed ratios to a common loaddevice.

It will also be observed that the optimum use has been made of thepre-heating principle in connection with the tertiary fluid. That is,the feed-water pumped into the mercury condenserboiler rst `picks upheat, at a comparatively low` It will also be r I 1y lower temperaturelevels. Also, except for the usual radiation and stack losses, the onlyrejection of heat from the cycle is to the condenser cooling water, at acomparatively low temperature level. Throughout the system, optimum useis made of the counter-flow heat transfer principle, both intransferring heat from the hot reaction products to the primary heattransfer fluid, from the primary fluid to the secondary and tertiaryworking fluids, and from various portions of the working fluid to theliquids at the cold sides of the working circuits. The resultingpowerplant promises to effect an overall thermal einciency substantiallygreater than that of previously known binary cycles using mercury andsteam while at the same time necessitating a much smaller charge of thecomparatively expensive mercury.

While the invention has been described as having uid circuits chargedwith sodium salts or liquid sodium metal, mercury, and water, it will beappreciated that other suitable operating, liquids might be used, forinstance, the highboiling point diphenyl compositions known to the tradeas Dow-Therm, the low-boiling chlorinated-fluorinated aliphatics knowncommercially as Freon, etc.

It will be obvious to those skilled in the art that many other minoralterations and substitutions of equivalent fluids and components mightbe made in the specific embodiment of the invention disclosed herein,and it is desired to cover by the appended claims all such modificationsas fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. In a three fluid thermal powerplant, the combination of conduitsdefining a primary liquid circuit charged with a material which remainsliquid at all normal operating temperatures and has a boiling jointsubstantially above the maximum temperature in the cycle and including aprimary heater connected by one supply conduit and one return conduit toa primary heat exchanger, the latter comprising rst heat exchange meansfor a secondary fluid circuit and second heat exchange means for atertiary duid circuit; conduits defining a secondary fluid circuitcharged with a high-boiling liquid and including an elastic uid turbinehaving in the exhaust conduit therefrom a secondary liquid pre-heaterreceiving heat from the spent secondary fluid and a condenser-boiler forcondensing the secondary vapor, and conduit means with a circulatingpump for passing secondary liquid from the condenser-boiler through theliquid pre-heater and then through the first `heat exchange means incounter-flow relation with the primary liquid, the secondary fluid vaporatertiary fluid circuit charged vvitha` compara-V tively; low-boilingliquid and including a' high pressure' and a low pressure elastic fluidturbine in series flow relation with-a second liquid preheater disposedin a second condenser receiving fluid exhausted from the lowpressure-turbine, and conduit means With a circulatingpump for passingcondensate from the-tertiaryv uid condenser through the second liquidpre-heater; thence through the-secondary liquid condenserboiler andthrough the third heat exchangemeans in counter-flow relation" withtheprimaryfluid and to the inlet of the high pressure turbine.

2. In a three fluid thermal powerplant; the combination of a primaryfluid circuit including aprimary heater and primary heati exchangermeans with onlyone high temperature conduit connecting the heater withthe exchanger and only one lower temperature return conduitr to theheater, the primary circuit being charged with a primary* liquid havinga boiling point substantially abovezthe maximum normal operatingtemperatures, aisurge tankconnected to the primary circuit andmaintained substantially at-ambient atmospheric pressure whereby-themaximuml pressure in the primary circuit. is only that of the hydraulichead of the liquid-in saidcircuit, the primaryheat-exchangerincludingrst, second, third, and fourth heat exchange devices in seriesflow relation, with thefirst devicereceiving the hot primary liquid',through the supply conduit directly from-the heater and the-fourthdevice discharging to the return line; a secondary fluid circuitincludingafirst elastic fluid-pressure turbine, said secondary circuitbeing charged with a high-boiling fluid'and closed to the atmosphere,fifth, sixth, and seventh-heat exchange devices associated with-thefirst turbine and adapted to extract heat from motive fluid exhaustedtherefrom, a secondary fluid circulating pump, and conduits defining avcircuit for the secondary fluid from the circulating pump through thelsixth heat exchange' device then through the second and first heatexchange devices serially and in counter-flow relation with the primarylliquid, the secondary fluid vapor from the hot discharge end of thefirst heat exchange device returning to the inlet of the first turbine;and a tertiary fluid circuitcharged with a comparatively low-boilingfluid-and including a second high pressure elastic fluid tur,- bine ofthe extraction type, and a third low pressure turbine having heated bythe exhaust therefrom an eighth heat exchange device-and a condenser forrejecting heat at the lowest temperature in the cycle to acoolant-fluid, said third fluid circuit including also condensatecirculating and boiler feed pump means and a' ninth heat exchange deviceheated by high temperature fluid extracted from the second turbine, andconduit means arranged to pass condensate from the condenser through theeighth heat exchange device in counter-flow relation with fluidexhausted from the third turbine, thence through the boiler feed pumpand the ninth heat exchange device, then through the seventh heatexchange device in counter-flow relation with the secondary fluid vaporexhausted from the first turbine, thence through the fifth heat'exchangedevice, and through the third heat exchange device in counter-flowrelation with the primary liquid,A thence to the inlet of the secondturbine, the exhaust from the second turbine vgoing through the fourthheat exchange deviceincounter-flow relation,- with` the primary liquidand thenceto the inlet of the-third turbine.

3. A- thermal powerplant, in accordance with claim .2 infw-hich theysecondary fluid turbine-and thehigh andlovv-` pressure tertiary fluidturbines are allgeared-to-drive a-common-load output device,the--gear-,ratios being'such that the secondary fluid turbine operatesat a--comparatively lowV speed; the .low pressure tertiary-z fluidturbine operates Aatan intermediate speed, and-the high pressure turbineoperates at a high speed.

4. In a threefluid thermal powerplant, the combination ofa-primaryliquid circuit charged Witha-material which is liquid at Vnormaloperating temperatures and Ahas-a boiling-point substantially= above`the maximum temperature inthe cycle and-including4 a primaryheaterconnected by: one supply conduit and one return conduit to aprimary heatexchanger comprisingfirst heat exchange means for the secondary fluid`circuit and. secondi-heat exchange means for the tertiary fluid circuit,the secondary-circuitbeing charged withahigh-.boiling liquid andvincluding an elasticfluidrturbine, a liquid pre-heater associated withthe secondary fluid turbine and adapted to be heated by the exhaustvapor therefrom, anda condenser-boiler for condensing secondary fluidin'thezsecondarycircuit andtransferring heat to the tertiary circuitlandconduit means with a circulating pumpv for passing Secondary liquidfrom the condenser-boiler through said preheater and then through `thefirst heat exchanger in counterflow. relation -With the primary liquid,vapor'from the'firstheatzexchange means returning to the inlet of thesecondary fluid turbine, the tertiary circuit beingcharged witha-loWer-boiling liquid and-including a highfpressure anda low-pressureelastic fluid turbine in series-flow relation with a tertiary fluidvcondenser receiving fluid from the lowA pressure turbine,4 circulatingpump f means with conduitmeans for passing condensatefrom the'tertiaryfluid condenser to the secondary fluid condenser-boiler; then throughthe third heat exchange means in counter-flow relation with thc primaryfluid and to the inlet ofthe high pressure turbine.

5. Afthree fluid thermal powerplant comprising conduitsdefining aprimaryliquid circuit charged with a material which is liquid at allnormal operating temperatures and has a boiling point substantiallyabove the maximum temperature in the cycle, conduits defining asecondary fluid circuit charged with ahigh-boiling liquid, and conduitsdefining a tertiary-4 circuit charged With a lowerboilingv liquid, theprimary circuit including a primary heater connected by one supplyconduit and'one return conduit to rst heat exchange means adapted tovaporize the liquid in the secondary circuit, means kin theprimary-circuit for preventing the staticpressure therein from risingsubstantially abovev ambient atmospheric pressure whereby the hightemperature primary circuit. is maintainedlat a comparatively lowpressure, the-secondary circuit including an elastic fluid-turbinehavingassociated with the exhaust therefrom a condenser-boiler adaptedto condense the secondary fluid in the secondary circuit and'vaporizeliquid in the tertiary circuit, the secondary circuit also includingpump means for passing liquid from the secondary fluid condenserthroughthe first heat exchanger in counter-now relation with the primaryliquid, conduits` for passing` secondary fluid Vapor from the firstheatexchangergto theinletof the secondary fluid turbine,- the=tertiarycircuit being charged with a comparatively low-boiling liquid andincluding at least one elastic fluid turbine having a condenser forreceiving the exhaust therefrom, circulating pump means in the tertiarycircuit with conduit means for passing condensate from the tertiary uidcondenser to the secondary uid condenserboiler, and conduit means forpassing tertiary fluid generated in the condenser-boiler to the inlet ofthe tertiary fluid turbine.

LEONARD R. BIGGS.

REFERENCES CITED The following references are of record in the le ofthis patent:

l UNITED STATES PATENTS Number Name Date Chesebrough June 29, 1886 GrebeNov. 15, 1932 Grebe Jan. 24, 1933 Thurm Aug. 15, 1933 Baumann Mar. 5,1935 Rosencrants July 13, 1937 Amiek Aug. 31, 1937 Larrecq Dec. 14, 1937Randel June 20, 1939 Lysholm Apr. 22, 1941 Mercier Apr. 12, 1949

